1. Technical Field
The present invention relates to an optical tomographic image photographing apparatus used to capture tomographic images of an object to be examined.
2. Related Art
An apparatus conventionally used to capture tomographic images of an object to be examined is an optical coherence tomography (OCT) device.
A known example of the optical coherence tomography device is a Fourier domain OCT device which captures tomographic images of an object to be examined through Fourier analysis of spectral information obtained by a light receiving element (see the Patent Document 1). As Fourier domain OCT devices, there are known SD-OCT where a spectroscopic optical system is provided in a light reception system, and SS-OCT where a wavelength-variable light source is provided in a light projection system.
A tomographic image obtained by an interference optical system based on the principle of Fourier domain OCT has an utmost photographic sensitivity (interference sensitivity) at a depth position where a measurement light and a reference light have an equal optical path length. The photographic sensitivity is more weakened with an increasing distance from the depth position. Therefore, a part of the image obtained near the depth position has a high photographic sensitivity and a high resolution, whereas other parts of the image obtained away from the depth position fail to have expected levels of sensitivity and resolution.
The apparatuses disclosed in the Patent Documents 1 and 2 are adapted to set different modes (retinal mode and choroidal mode); one mode is to output a tomographic image captured when fundus is located behind the depth position where the optical path lengths of the measurement and reference lights become equal (normal image), while the other mode is to output a tomographic image captured when fundus is located ahead of the depth position where the optical path lengths of the measurement and reference lights become equal (reverse image).